The present invention relates to a fluidized bed apparatus used in the production of fine particles, granules, etc. of pharmaceutical preparations, agricultural chemicals, food products, etc., and more specifically to a fluidized bed apparatus suitable for coating processing on particles of a fine particle size or granulation processing of particles with a fine final particle size.
A fluidized bed apparatus generally performs granulation or coating by spraying a spray solution (coating solution, binder solution, etc.) from a spray nozzle while forming a fluidized bed of powder particles within a processing container by using fluidizing gas introduced from the bottom of the processing container. Of the fluidized bed apparatuses of this type, those involving rolling, jetting, stirring, etc. of the powder particles are referred to as a compound fluidized bed apparatus.
FIG. 8 shows a fluidized bed apparatus (commonly called “Wurster type fluidized bed apparatus”) equipped with a draft tube 5′. The fluidized bed apparatus has the draft tube 5′ installed in the central portion of a processing container 3′. Particles are carried by an air current ascending within the tube 5′, thus generating an upward flow (jet layer) of the particles. A spray solution of film agent, pharmaceutical agent, or the like is sprayed upwardly from a spray nozzle 6′ installed at the bottom center of the processing container 3′ toward the particles in the tube 5′. The fluidized bed apparatus of this type, which allows a large amount of particles to be sent into the coating zone at high speed, is relatively free from the spray dry phenomenon or secondary agglomeration of particles, thus enabling coating processing on fine particles at good yield (refer to JP 2000-62277 A, for example).
In a fluidized bed apparatus, a generally adopted means for controlling the cohesiveness between particles, which results from the stickiness or tackiness of the base components of a spray solution, is to set (during the coating operation) the spray rate of the spray solution to a low level where no secondary agglomeration will occur between the particles, or to set (during the granulating operation) the spray rate of the spray solution to a low level where the particles do not form an aggregate due to excessive agglomeration. However, this involves many problems in terms of product manufacture costs, such as the prolonged processing time due to the low spray rate of the spray solution or the necessity of performing numerous experiments to grasp the characteristics of the spray solution prior to setting the spray rate of the spray solution.
Often adopted as another such means is to disperse agglomerated particles by the jet force of compressed air. However, to attain the anticipated effect, it is necessary to spray considerably high-pressure compressed air from a number of spray nozzles, which disadvantageously increases the consumption of air not contributing to the drying of particles.
Further, it has been practically difficult, even by optimizing the spray rate of the spray solution or by dispersing particles with compressed air, to effect coating processing on particles having a fine particle size, for example, fine particles with a particle size of 100 μm or less, particularly those with a particle size of 50 μm or less, without involving secondary agglomeration, or to produce product particles with a sharp particle size distribution in granulation processing for obtaining the above-mentioned particle sizes as the final particle sizes.